It is much easier if you can install Vista first. then install Mint from a live CD using the "directed-use largest contiguous space" option in the disk partitioner. This will allow you to size your Mint partition by using the graphic of the disk and sliding the partition to the size you want. If your Mint installation has not grown too large, I would suggest dumping your current install, installing Vista, then reinstalling Mint.
Another advantage of installing Vista first is when Mint is installed, Grub will pick up the Vista partition and set up the dual boot menu automatically. No messing with EasyBCD or reinstalling Grub from the live CD
. Of course I can't know your situation. If you have things in your current Mint install you don"t want to lose then of course you should continue with installing Vista as you plan. If this is the case, I think you may not have the identical hard disk set up as the author of the guide. What you have to do is identify the newly created space by size as well as disk location. When you are sure you have the correct partition located, proceed with the installation process using Diskpart to activate the partition.
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